Your contacts, email, calendar, and your photos are some of your most personal data. When an app wants your data, either for processing or uploading, it will tell you the first time.
You can change each app's access by going to Settings > Privacy and select each app, like Contacts, and swipe on or off which third-party apps you want to grant access to.
If you have already granted an app access to your data, switching off the service on your device does not mean that service will delete your data. You will have to contact that company or app maker for this.